Non-Simplified SUSY: Stau Coannihilation at LHC and...

Non-Simplified SUSY: Stau Coannihilation

at LHC and ILC

M. Berggren, A. Cakir, D. Krücker, J. List, A. Lobanov, I.-A. Melzer-Pellmann

Linear Collider Forum

DESY 2013

Isabell-A. Melzer-Pellmann LC Forum – DESY 2013 2

Outline

! Introduction ! LHC Analyses ! ILC Analyses ! Summary

Isabell-A. Melzer-Pellmann LC Forum – DESY 2013

Storyline

! What if LHC sees some kind of signal, but cannot distinguish between ! Is it SUSY or other BSM models? ! Is it more than one new particle? ! What are the masses and other properties of the new particles? ! Can LHC distinguish between different production processes? ! Do we see THE dark matter?

! Can ILC add information and see particles that LHC cannot see (or at least not distinguish)?

à LHC: discovery of colored states à  ILC: precise measurement of EW states

3


Storyline

! Choose a full model that is compatible with all recent observations, e.g.: ! Higgs @ 125 GeV ! Relic density ! Latest results of direct dark matter searches

! Full model chosen as example here: SUSY pMSSM model with small mass difference (10 GeV) between stau and LSP

•  Four models with differing stop masses:

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Model name Mass parameter of right-handed top quark / GeV

Stop mass / GeV

STC4 400 293

STC5 500 416

STC6 600 527

STC8 800 736


Full Spectrum STC4

! Low stop mass à large direct stop production cross section

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Full Spectrum STC5

! Relatively low stop mass à direct stop production cross section much smaller than in STC4

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Full Spectrum STC6

! EWkino production gains more weight

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Full Spectrum STC8

! EWkino production has largest cross section

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Lower part of STC8 Spectrum

! Many different decays at lower masses

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Cross sections for all models (LHC)

! Inclusive cross sections ! LO calculated with Pythia6 ! NLO calculated for most

sub-processes with Prospino2.1

! STC4 dominated by direct stop production

! EWkino cross sections quite dominating in the other scenarios

! 33 TeV cross section to be taken with some caveat – PDFs not known here…

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Sub-process cross sections for STC8

! NLO calculated where possible

! Gluino-gluino production ~0.2 fb à expect ~600 events at 3000 fb-1

! Direct production of first 2 generations ~20fb à 60.000 events à expect more sensitivity for these (e.g. search for high-energetic jets and MET, no b-tags)

! EWkino production dominates

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Where we are…



[GeV]1

t~m

200 300 400 500 600 700

[G

eV

]0 1χ∼

m

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forb

idde

n

1±χ∼

b→1t~

) = 5 GeV1

0χ∼) - m(1

±χ∼, m(1

±χ∼ b→1t~

production, 1t~-1t

~

ATLAS Preliminary

=8 TeVs, -1

L dt = 12.8 fb∫

)theorySUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

All limits at 95% CL

Figure 3: Expected and observed 95% C.L. exclusion limits in the mt̃1 −mχ̃01plane for ∆m = 5

GeV. The black, dashed line shows the expected limit if theoretical uncertainties on the signalare neglected. The yellow band shows the±1σ uncertainty on the expected limit. The red solidline shows the nominal observed limit, while the red dashed lines show its variation if theoryuncertainties on the signal are taken into account.

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Reach of current 8 TeV Analyses

! Full-hadronic analysis from ATLAS: ATLAS-CONF-2013-001 ! m_stop = 293 GeV and m_N1 = 95 GeV lies in excluded region, but…

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STC4



! Full-hadronic analysis from ATLAS: ATLAS-CONF-2013-001

à No observation with current analysis expected

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! CMS EWkino Analysis PAS-SUS-12-022 ! Mass parameters outside excluded

region for case with stau mass in middle of C1 and N1 (even worse if stau closer to N1)

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[GeV]02χ∼

=m±

1χ∼

m100 150 200 250 300 350

[G

eV]

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]σ

95%

CL

uppe

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it on

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410-1 = 9.2 fbint = 8 TeV, LsCMS Preliminary

95% C.L. CLs NLO Exclusionstheory

σ 1 ± lObserved 3theory

σ 1 ± lExpected 3

02χ∼ ±

1χ∼ → pp

τντ∼ → ±

1χ∼

ττ∼ → 02χ∼

01χ∼

+ 0.5m±

1χ∼

= 0.5ml~ m

[GeV]02χ∼

=m±

1χ∼

m100 200 300 400 500 600 700 800

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eV]

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> m

±1χ∼

= m

02χ∼m

-1 = 9.2 fbint = 8 TeV, LsCMS Preliminary


σ 1 ± lObserved 3theory

σ 1 ± lExpected 3

02χ∼ ±

1χ∼ → pp

τντ∼ → ±

1χ∼

ττ∼, µµ∼, ee~ → 02χ∼

) = 1-l+l~ → 02χ∼(Br

01χ∼

+ 0.5m±

1χ∼

= 0.5ml~ m [GeV]02χ∼

=m±

1χ∼

m100 200 300 400 500 600 700 800

[G

eV]

0 1χ∼m

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]σ

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uppe

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> m

±1χ∼

= m

02χ∼m

-1 = 9.2 fbint = 8 TeV, LsCMS Preliminary


σ 1 ±+SS lObserved 3theory

σ 1 ±+SS lExpected 3 onlylObserved 3

Observed SS only

02χ∼ ±

1χ∼ → pp

τντ∼ → ±

1χ∼

ττ∼, µµ∼, ee~ → 02χ∼

) = 1-l+l~ → 02χ∼(Br

01χ∼

+ 0.95m±

1χ∼

= 0.05ml~ m

STC4-8


LHC: Search for Stops (0 leptons)

! Simple cut-and-count analysis, inspired by ATLAS 8 TeV full-hadronic analysis: ! Lepton veto (no identified lepton with pT > 10 GeV) ! N_jets > 3

! Jet1: pT > 120 GeV ! Jet2: pT > 70 GeV ! Jet3: pT > 60 GeV

! N_btag >= 2 ! HT > 1000 GeV ! dΦ(MET, Jet1,2) > 0.5 ! MET/Meff > 0.2 ! MET > 750 GeV

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! Control plots before cut on MET, MET/Meff, Δφ(Jet1,2 and MET):

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! Discovery and exclusion sensitivity depends on systematic uncertainty

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! Full-hadronic search reaches 5σ discovery only for STC4 and systematic uncertainty of ~15%:

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LHC: Search for Stops (1 lepton)

! Simple cut-and-count analysis, inspired by ATLAS 8 TeV full-hadronic analysis: ! Exactly one e/µ with pT > 10 GeV, veto 2nd e/µ with pT > 10 GeV) ! N_jets > 3, with pT > 40 GeV ! N_btag = 1 or 2 ! dΦ(MET, Jet1,2) > 0.5 ! MET > 500 GeV ! HT > 500 GeV ! MT > 120 GeV

! MT2W > 250 GeV

or topness > 9.5, pT asymmetry (lepton, jet1) > -0.2

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topness: see arXiv:1212.4495



! Control plots before cut on lepton and jet requirements: MT and lepton pT after the MT requirement

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! Discovery and exclusion sensitivity depends on systematic uncertainty

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LHC: Search for Stops

! Single-lepton search reaches 5σ discovery only for STC4 and STC5 and systematic uncertainty of ~15% with 300 fb-1, High Lumi LHC (3000 fb-1) needed for discovery of all four models:

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LHC: Search for EWkinos

! Search for same-sign leptons coming from: ! N2 C1 production, where

! N2à stau tau à tau tau N1 ! C1 à tau N1

! expect at least same-sign + additional lepton

! Rough comparison to same-sign analysis in PAS CMS-12-022 ! 8 TeV signal yields less than 10 Events for STC4 (where 11 are observed in

data and compatible with BG expectation)

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LHC: Search for EWkinos

! Need to reduce systematic uncertainties to exclude EWKinos, 5σ discovery hardly possible if uncertainty larger than 15%

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LHC Search – Conclusion

! High Lumi LHC will be able access all four models with 3000 fb-1, but:

! it will be difficult to identify the nature of the access ! EWkino sector will be difficult to see with more than 3σ ! staus very difficult for LHC ! will need ILC to further identify particle masses etc.

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Where we are…



ILC: Precision Measurement

! At ILC (@ 500 GeV), all sleptons and bosinos can be produced with reasonable cross section (inclusive for both polarizations about 3pb)

! Full lines: P(e+e−) = (−0.3,+0.8) ! Dashed lines: P(e+e−) = (+0.3, −0.8)

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0

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0 100 200 300 400 500 600 700 800 9001000Ecms [GeV]

σ [f

b]

TDR4Solid : RLDashed : LR

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10 2

10 3

0 100 200 300 400 500 600 700 800 9001000Ecms [GeV]

σ [f

b]

TDR4Solid : RLDashed : LR


ILC: Stau_1 Measurement

! Very clean signal after few cleaning cuts ! Stau_1 can be measured with precision of 200 MeV

endpoint determination cross section determination using region between arrows

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[GeV]jetE0 20 40 60

jets

/0.7

Gev

1

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310 Signal SM BG SUSY BG

) [GeV]jet

Max(E0 10 20 30 40 50

even

ts/0

.5 G

eV

0

50

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150


ILC: Stau_2 Measurement

! Not only stau_1, but also stau_2 can be measured with high precision up to 5 GeV:

endpoint determination cross section determination using region between arrows

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[GeV]jetE0 50 100 150

jets

/1.8

GeV

0

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400

600

800

Signal SM BG SUSY BG

) [GeV]jet

Max(E0 50 100 150ev

ents

/1.8

GeV

0

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ILC: Measurement of smuon

! Reconstruction of invariant di-muon mass à edge for smuon

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[GeV]µµm0 50 100 150 200 250 300 350 400 450 500

)-1

Yiel

d (5

00 fb

02000400060008000

10000120001400016000 1)×Standard Model Background (

10)×SUSY background(

100)× (01χµµ → µµ∼ → 0

2χ 0

1χ →-e+e

10)× (01χ µ 0

1χ µ→

L

-µ∼+

Lµ∼ →-e+e


[GeV]µµm0 50 100 150 200 250 300 350 400 450 500

)-1

Yiel

d (5

00 fb

02000400060008000



100)× (01χµµ → µµ∼ → 0

2χ 0

1χ →-e+e

10)× (01χ µ 0

1χ µ→

L

-µ∼+

Lµ∼ →-e+e


! Reconstruction of invariant di-muon mass à edge for smuon

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/ ndf = 20.57 / 262χBackground(B) 2.93± 55.22 Edge (E) 0.0± 82.5 Width (S) 0.402± 1.747 Signal Amplitude (A) 5.8± 47.1 Signal Tail (T) 0.0785± 0.2713 Background Exp (BE) 0.0647± 0.9554 Background Slope (BS) 5.61± -79.82

Invariant Mass [GeV]40 50 60 70 80 90

)-1

Yiel

d (5

00 fb

020406080

100120140 / ndf = 20.57 / 262χ

Background(B) 2.93± 55.22 Edge (E) 0.0± 82.5 Width (S) 0.402± 1.747 Signal Amplitude (A) 5.8± 47.1 Signal Tail (T) 0.0785± 0.2713 Background Exp (BE) 0.0647± 0.9554 Background Slope (BS) 5.61± -79.82

Standard Model BackgroundSUSY background

01χµµ → µµ∼ → 0

2χTotal signal



! Mu energy spectrum (smu_L)

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energy [GeV]µ0 50 100 150 200 250

)-1

Yiel

d (5

00 fb

0

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100)× (01χµµ → µµ∼ → 0

2χ 0

1χ →-e+e

10)× (01χ µ 0

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L

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+Lµ∼ →-e+e


ILC: Measurement of smuon_L

! Mu energy spectrum (smuon_L)

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energy [GeV]µ0 50 100 150 200 250

)-1

Yiel

d (5

00 fb

0

2000

4000

6000

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10000



100)× (01χµµ → µµ∼ → 0

2χ 0

1χ →-e+e

10)× (01χ µ 0

1χ µ→

L

-µ∼

+Lµ∼ →-e+e / ndf 2χ 29.73 / 26

Amplitude(A) 2.94± 48.92 Edge (E) 0.04± 32.25 Slope (S) 1.10605± 0.03249 Background (B) 1.65± 38.21

energy [GeV]µ26 28 30 32 34 36 38 40 42

)-1

Yiel

d (5

00 fb

2030405060708090

100110

/ ndf 2χ 29.73 / 26Amplitude(A) 2.94± 48.92 Edge (E) 0.04± 32.25 Slope (S) 1.10605± 0.03249 Background (B) 1.65± 38.21

B+A/(1+exp(x-E)/S)

signal

/ ndf = 8.39 / 142χAmplitude(A) 3.51± 43.97

Edge (E) 0.2± 151.5

Slope (S) 0.1233± 0.3775

Background (B) 1.53± 15.17

energy [GeV]µ146 148 150 152 154 156

)-1

Yiel

d (5

00 fb

10203040506070

/ ndf = 8.39 / 142χAmplitude(A) 3.51± 43.97

Edge (E) 0.2± 151.5

Slope (S) 0.1233± 0.3775

Background (B) 1.53± 15.17

B+A/(1+exp((x-E)/S))

Signal


ILC: Measurement of Tau Helicity

! Tau polarization: depends on ! mixing angle θstau of the chiral eigenstates to mass eigenstates ! amount of Higgsino and gaugino eigenstates of N1 (gaugino and fermions:

conserving chirality; Higgsino: Yukawa coupling flips chirality)

! Ratio of pion over jet energy differs for different tau helicity both tau leptons opposite both tau leptons right-handed helicity left-handed

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Jet / EπE0 0.2 0.4 0.6 0.8 1

ratio

/ 0.

01

0

0.01

0.02

0.03

0.04

0.05 entries6 10⋅inital spectrum: 0.507

entries6 10⋅selected spectrum: 0.170

a)

Jet / EπE0 0.2 0.4 0.6 0.8 1

ratio

/ 0.

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0

0.005

0.01

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entries6 10⋅inital spectrum: 1.014


b)

Jet / EπE0 0.2 0.4 0.6 0.8 1

ratio

/ 0.

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0.01

0.015

0.02

0.025

entries6 10⋅inital spectrum: 0.507


c)

Figure 15: Distribution of R = Eπ/Ejet before (open histogram) and after event selection(grey (yellow) histogram). a): both τ leptons are right-handed. c): the τ leptons haveopposite helicity. r): both τ leptons are left-handed.

Jet / EπE0 0.2 0.4 0.6 0.8 1

entri

es /

0.02

0

100

200

300

400

0.05)± = (0.86 FitτP

/ndf = 17 / 35 2χ

simul. data points

fit to data

Figure 16: The distribution of R = Eπ/Ejet in the selected sample. The line shows thefitted efficiency and background corrected model.

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Dark Matter

! Prediction of the relic density based on the assumption that the χ10 is the

only contribution to Dark Matter

! LHC alone can never reach precision as LHC+ILC ! ILC has high predictive power also for MSSM with 18 parameters

(compared to mSUGRA with 4 parameters)

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Where we are…



Summary and Conclusion

! LHC capable to observe all four studied models due to discovery of the light third generation squarks

! Gluino measurement difficult due to low cross section ! Sensitivity to EW sector at LHC very low due to challenging stau decays –

sensitivity depends on control of systematic uncertainty à  Need ILC for precision measurements of the EW sector

à At ILC all sleptons and bosinos with masses low enough to be produced with ILC energy have reasonable cross section to be measured, e.g.:

à Mass measurements of stau_1 and stau_2 à Mass measurements of smuons à Measurement of tau helicity

à  ILC needed for Dark Matter question!

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[GeV]jetE0 20 40 60

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Non-Simplified SUSY: Stau Coannihilation at LHC and...

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